Geomembranes are thick sheets for use in various applications like liquid containment, covers for reservoirs, water conveyance liners, landfill liners and caps. A LLDPE geomembrane for landfill caps must meet the Geosynthetic Research Institute, (GRI) requirements, such as tensile strength at break (psi or MPa), tensile elongation at break (%) and multi-axial requirements. In addition, the resin must process well, have good melt strength, preferably without blending with other resins, and have improved performance at lower cost.
International Publication No. WO 2006/067180 discloses a geo-membrane, produced by flat sheet extrusion or by blown sheet extrusion, with a bimodal resin consisting of medium density polyethylene (MDPE) having a density from 0.925 to 0.945 g/cc. In one embodiment, the MDPE resin is prepared by chemical blending using a single metallocene catalyst system in a double loop reactor.
U.S. Pat. No. 6,355,733 discloses a blend comprising a high molecular weight, medium density polyethylene (HMW, MDPE) and a linear low density polyethylene (LLDPE). The blend comprises from about 20 wt % to about 80 wt % of HMW MDPE. The HMW MDPE has a density from about 0.92 to about 0.944 g/cc, a melt index MI2 from about 0.01 to about 0.5 dg/min, and a melt flow ratio MFR from about 50 to about 300. The blend also comprises about 20 wt % to about 80 wt % of LLDPE. The LLDPE has a density within the range of about 0.90 to about 0.925 g/cc, and an MI2 within the range of about 0.50 to about 50 dg/min. The blend is disclosed as providing films with significantly improved toughness and tear strength, compared to MDPE or HDPE, and high modulus compared to LLDPE.
International Publication No. WO 2004/016688 discloses a polyethylene composition that has a density of about 0.945 to about 0.960 g/cc, and a melt flow index of about 0.1 to about 0.4. The composition is a melt blend of a linear low density polyethylene resin and/or a linear medium low density polyethylene resin, and a high density polyethylene resin.
U.S. Pat. No. 6,187,423 discloses a peroxide treated LLPDE material that can used as a geomembrane liner in land areas storing toxic waste, municipal landfills, leachate or slurry ponds, and other such land containment applications, as well as applications that require a strong, non-biodegradable material, which is impermeable to air and moisture.
Irrigation systems have evolved over the past 50-years from flood irrigation to the increased use of sprinklers and micro-irrigation systems. The main driver for such systems is the global focus on water conservation due to droughts, raising environmental awareness, and a high U.S. daily demand for water (billions of gallons each day).
There is a need for micro irrigation systems, based on cost-effective ethylene-based polymers, not costly post reactor blends or in-situ reactor blends, and which have sufficient or improved hydrostatic and mechanical properties. The typical ISO rated materials used are PE 32 and PE 40, which are both polyethylene based materials, or the PE 1404 resin per the American Standards Test Methods (ASTM).
Linear low density polyethylene (LLDPE) is preferred for micro tubing over high density polyethylene because of the lower flexural modulus. Micro tubing based on LLDPE can be “hole-punched” for efficient manipulation and repairs in the field of operation. In addition, the flexibility of tubing based on LLDPE allows for coiling of the tubing, without kinking, throughout the irrigated area. However, typical LLDPE resins need to be blended with higher density polyethylenes to improve hydrostatic strength.
U.S. Patent US20070273066A1 discloses a multimodal linear low density polyethylene composition for the preparation of a pressure pipe. The composition is prepared in-situ, and has a density of 910-940 kg/m3, an E-modulus in the range of less than 800 MPa, an abrasion resistance of less than 20, and a melt index (MFR2) of less than 2 g/10 min. This product requires multiple reactors to make the different LMW and HWM fractions for the final multimodal composition.
U.S. Pat. No. 5,455,303 discloses a polymer composition of the following: (A) a polyolefin composition consisting essentially of (i) a linear low density polyethylene and (ii) a copolymer of propylene with ethylene and/or a C4-C8 α-olefin, where R is an alkyl radical having 2 to 10 carbon atoms, and (B) a low density polyethylene. This composition comprises a blend of the two resins, which adds to the cost of this product.
International publication WO2005/097888A1 discloses a blend comprising from 70 to 98 weight percent of a chromium-based polyethylene resin, based on the total weight of the blend, and from 2 to 30 weight percent of a bimodal polyethylene resin having a density of from 0.940 to 0.965 g/cc, and an ESCR that is at least 10 times larger than that of a chromium-based resin of equivalent density, and prepared either with a Ziegler-Natta or with a metallocene catalyst system. The blend is disclosed as having improved environmental stress crack resistance and good processing behavior, with no loss of rigidity. Again, blending adds to the overall cost of the final resin.
Additional ethylene-based polymers, blends and/or compositions, and articles formed from such, are disclosed in International Publication Nos. WO 01/98409; WO 04/016688; WO 08/051,824; WO 08/153,586; U.S. Publication Nos. 2006/0122362; 2007/0078225; 2005/0245689; 2010/0003439; and U.S. Pat. Nos. 5,221,570; 6,187,423; and 6,355,733.
There is a need for cost-effective ethylene-based polymers that are not costly free-radical treated polymers or costly bimodal blends, and yet have sufficient or improved melt properties and mechanical properties for geomembrane applications. There is also a need for irrigation tubing formed from low cost ethylene-based polymers, not costly treated polymers or costly post reactor blends or in-situ blends, and which has sufficient or improved hydrostatic and mechanical properties for micro irrigation applications. These needs have been met by the following invention.